The present invention relates to a selective calling/receiving device which is equipped with a compact battery and intermittently performs a receiving operation through use of a timing signal generation circuit.
FIGS. 4A and 4B are schematic representations for explaining receiving timing of an existing selective calling/receiving device. In FIGS. 4A and 4B, the duration of a data segment to be received by the selective calling/receiving device is as short as 1.875 sec. for example, and the data segments to be received are transmitted at long intervals, for example, every 30 sec. For these reasons, the selective calling/receiving device intermittently performs a receiving operation in order to receive only the required data segments, thereby increasing the life of a battery. In order to cause the selective calling/receiving device to intermittently perform a receiving operation in the manner as mentioned previously, it is necessary to determine the control timing of intermittent receiving operations, in consideration of a period of time (i.e., pre-heat time) during which the device becomes possible to receive a data segment after having received power from the power source. Generally, a receiver requires a longer pre-heat time when a receiving electric-field strength is weak, and the timing of intermittent operation of the receiver is controlled such that the receiver starts up under the worst conditions.
Referring to FIG. 5, the configuration and operation of an existing selective calling/receiving device will be described. A high-frequency signal converted into an electrical signal by means of an antenna 1 is amplified by a high-frequency amplifying circuit 2, where the amplified signal is output to a frequency conversion circuit 3. An electric field level detection circuit 8 determines the level of the signal output from the frequency conversion circuit 3 and outputs the result of such determination to an automatic gain setting circuit 9 which sets the gain of the high-frequency amplifying circuit 2. The calling characteristics of the calling/receiving device in a strong electric field are made stable by feeding back the result of such setting to the high-frequency amplifying circuit 2. The output from the frequency conversion circuit 3 is demodulated by a demodulation circuit 4, where transmission data are demodulated. The internal timing of the calling/receiving device is synchronized to the timing of transmission data by means of a synchronization circuit 5, using the demodulated data received from the demodulation circuit 4. A timing signal generation circuit 10 determines the timing of intermittent operation of the calling/receiving device, using the internal timing synchronized to the transmission data. A comparison circuit 6 compares a received selective call number with the selective call number of the calling/receiving device. If there is a match between the numbers, a notification circuit 7 notifies the user of an incoming call, using sound, vibration, or an indication. The timing signal generation circuit 10 determines the timing of intermittent operation of the calling/receiving device from the result received from the synchronization circuit 5, and the pre-heat time of the calling/receiving device is determined in such a way that the receiver starts up under the most undesirable conditions of electric field, e.g., in a weak electric field.
As mentioned previously, since the pre-heat time of the existing selective calling/receiving device for use with a mobile communications terminal is set so as to start up under the most undesirable conditions, the setting of the calling/receiving device is undesirable in terms of the life of the battery.